Alteration or reversal of the cyclic and progressive results of myocardial ischemia is a dilemma in myocardial pathophysiology. This study attempts to quantitate regional and transmural patterns in myocardial blood flow in the anoxic working heart with and without the benefit of a membrane stabilizer - methylprednisolone as used in this study. Regional and transmural myocardial blood patterns were determined in four groups of dogs before LAD coronary artery occlusion and after removal of the LAD occlusion. Groups I and II were controls having a one hour and two hour occlusion respectively before reflow patterns were determined. Groups III and IV were studied similarly, except that methylprednisolone was given one time in a pharmocologic dose prior to the LAD occlusion in each animal. Patterns of regional and transmural myocardial blood flow were determined by the radioactive microsphere technique and a vital dye - thioflavin-S. Group I reflow pattern was that of progressively decreased flow from epicardium to endocardium, even though the total transmural flow was normal. Group II was worsened. The total transmural flow was decreased, and the transmural maldistribution of Group I was further accentuated. Furthermore, the total size of the ischemic area was increased. Group III reflow pattern was almost normal regionally and transmurally, indicative of only reversible metabolic events. Group IV reflow was similar to that of Groups I and II.